WO2006022107A1

WO2006022107A1 - Power factor improving circuit

Info

Publication number: WO2006022107A1
Application number: PCT/JP2005/013623
Authority: WO
Inventors: Mamoru Tsuruya
Original assignee: Sanken Electric Co., Ltd.
Priority date: 2004-08-27
Filing date: 2005-07-26
Publication date: 2006-03-02
Also published as: CN1906839A; CN100541995C; US7466110B2; US20070103949A1; JP2006067730A

Abstract

A power factor improving circuit includes: a boosting reactor (L1) for inputting rectified voltage obtained by rectifying the AC power voltage of an AC power source (Vac1) by using a rectification circuit (B1); a main switch (Q1) turning ON/OFF by inputting the rectified voltage via the boost reactor (L1); conversion units (D1, C1) for converting the voltage obtained by turning ON/OFF of the main switch (Q1) into a DC output voltage; and a control circuit (10) controlling ON/OFF of the main switch (Q1) so as to make the AC power current into sinusoidal wave shape, controlling the output voltage of the conversion units (D1, C1) into a predetermined voltage, and controlling the switching frequency of the main switch (Q1) according to the value of the current flowing in the AC power source (Vac1) or the current flowing in the rectification circuit (B1) or the current flowing in the main switch (Q1).

Description

Specification

Power factor correction circuit

Technical field

The present invention relates to a power factor correction circuit used for a switching power supply with high efficiency, low noise, and high power factor.

Background art

FIG. 1 is a circuit configuration diagram of a conventional power factor correction circuit described in Japanese Patent Publication No. 2000-37072. In the power factor correction circuit shown in Figure 1, the output switch PI1 and P2 of the full-wave rectifier circuit B1 that rectifies the AC power supply voltage of the AC power supply Vacl are connected to the main switch Q1 and the current detection resistor R. A series circuit consisting of A series circuit that also has a force with a diode D1 and a smoothing capacitor C1 is connected to both ends of the main switch Q1. A load RL is connected to both ends of the smoothing capacitor C1. The main switch Q1 is turned on by the control circuit 100 PWM (Pulse Width Modulation) control. The current detection resistor R detects the input current flowing through the full-wave rectifier circuit B1.

The control circuit 100 includes an error amplifier 111, a multiplier 112, an error amplifier 113, an oscillator (OSC) 114, and a PWM comparator 116.

In error amplifier 111, reference voltage E1 is input to the + terminal, and the voltage of smoothing capacitor C1 is input to the-terminal. The error amplifier 111 generates an error voltage signal by amplifying an error between the voltage of the smoothing capacitor C1 and the reference voltage E1, and outputs the error voltage signal to the multiplier 112. The multiplier 112 multiplies the error voltage signal from the error amplifier 111 by the full-wave rectified voltage from the positive-side output terminal P1 of the full-wave rectifier circuit B1, and outputs the multiplied output voltage to the + terminal of the error amplifier 113.

In error amplifier 113, a voltage proportional to the input current detected by current detection resistor R is input to one terminal, and a multiplication output voltage from multiplier 112 is input to the + terminal. The error amplifier 113 amplifies the error between the voltage generated by the current detection resistor R and the multiplied output voltage, generates an error voltage signal, and outputs this error voltage signal to the PWM comparator 116 as a feedback signal FB. OSC (Oscillator) 114 generates a triangular wave signal with a fixed period [0006] In the PWM comparator 116, the triangular wave signal from the OSC 114 is input to one terminal, and the feedback signal FB from the error amplifier 113 is input to the + terminal. The PWM converter 116 is turned on when the value of the feedback signal FB is greater than or equal to the value of the triangular wave signal, and generates a pulse signal that is turned off when the value of the feedback signal FB is less than the value of the triangular wave signal. The pulse signal is applied to the gate of the main switch Q1.

That is, the PWM comparator 116 provides a duty pulse corresponding to a difference signal between the output of the current detection resistor R by the error amplifier 113 and the output of the multiplier 112 to the main switch Q1. This duty pulse is a pulse width control signal that continuously compensates for fluctuations in the AC power supply voltage and the DC load voltage at a constant period. With such a configuration, the AC power supply current waveform is controlled to match the AC power supply voltage waveform, and the power factor is greatly improved.

FIG. 2 is a timing chart of the AC power supply voltage waveform and the rectified output current waveform of the conventional power factor correction circuit. FIG. 3 shows details of part A of the timing chart shown in FIG. In other words, Fig. 3 shows the switching waveform of lOOKHz near the maximum value of the AC power supply voltage. FIG. 4 shows details of part B of the timing chart shown in FIG. That is, Fig. 4 shows the lOOKHz switching waveform at the low AC power supply voltage.

Next, the operation of the power factor correction circuit configured as described above will be described with reference to the timing chart shown in FIG. Fig. 3 shows the voltage Qlv across the main switch Q1, the current Qli flowing through the main switch Q1, and the current Dli flowing through the diode D1! /.

[0010] First, at time t, the main switch Ql is turned on, and the full-wave rectifier circuit B1

31

Current Qli flows to main switch Q1 via torr L1. This current is

32

It increases linearly over time. From time t to time t, diode D1

31 32

The flowing current Dli becomes zero.

[0011] Next, at time t, the main switch Q1 also changes the on-state force to the off-state. This

32

The voltage Qlv of the main switch Q1 rises due to the energy stored in the boost reactor L1. Also, from time t to time t, the main switch Q1 is off, so the main switch Q1

32 33

The current Qli that flows through is zero. From time t to time t, B1 → L1 → D1 → C1 The current Dli flows along the path of R → B1, and power is supplied to the load RL. Disclosure of the invention

[0012] By the way, normally, in order to reduce the size of the boost reactor L1, it is necessary to set the frequency to a high frequency (for example, 100 kHz). However, even if the frequency is high, the magnitude of the current corresponding to the vicinity of the maximum value of the AC power supply voltage, the energy stored in the boost reactor L1 in part A, is the diode D1 when the main switch Q1 is turned off. To be supplied to the load RL.

[0013] However, in the low voltage part such as B part, the current is small and the current when the main switch Q1 is turned off is low. Also, the main switch Q1 made of MOSFET has an internal capacitance (parasitic capacitance) not shown. Main switch Q1 has internal capacitance C

0 and voltage applied to main switch Q1

Power loss is generated by the amount determined by V (CV ² Z2). This power loss is the frequency

0

It increases in proportion to the number.

[0014] Further, due to the internal capacity of the main switch Q1, less energy is stored in the boost rear reactor L1. For this reason, the voltage Qlv when the main switch Q1 is turned off becomes a sine wave as shown in FIG. 4, does not increase to the output voltage, and the power loss increases. That is, the efficiency is lowered.

[0015] The present invention can reduce the power loss in the low-frequency part by reducing the switching frequency or stopping the operation in the low-input current part, and can achieve small size, high efficiency, and low noise. An object of the present invention is to provide a power factor correction circuit.

[0016] The power factor correction circuit according to the present invention inputs a rectified voltage obtained by rectifying an AC power supply voltage of an AC power supply using a rectifier circuit, and inputs the rectified voltage via the boosted rear tuttle to turn on and off. A main switch, a converter that converts the voltage obtained by turning on and off the main switch to a DC output voltage, and an on-off control of the main switch to make the AC power supply current sinusoidal. Control for controlling the output voltage of the converter to a predetermined voltage and controlling the switching frequency of the main switch according to the value of the current flowing through the AC power supply, the current flowing through the rectifier circuit, or the current flowing through the main switch. Part.

[0017] Further, the power factor correction circuit of the present invention is connected to the main power line and the main power line in series, and A booster reactor having a feedback feeder that is loosely coupled to the main feeder, and connected between one output terminal of the rectifier circuit that rectifies the AC power supply voltage of the AC power supply and the other output terminal; A first series circuit comprising the main power line, the first diode and a smoothing capacitor; and connected between the one output terminal and the other output terminal of the rectifier circuit, and A second diode connected between a connection point between the main switch and the feedback feeder of the step-up rear tuttle and the smoothing capacitor. By turning on and off the main switch, the AC power supply current is made sinusoidal, the output voltage of the smoothing capacitor is controlled to a predetermined voltage, and the switching frequency of the main switch is changed to the alternating current. And a control unit for controlling in accordance with the value of the current flowing through the current or the main switch through the current or the rectifier circuit through the power supply.

Brief Description of Drawings

FIG. 1 is a circuit configuration diagram showing a conventional power factor correction circuit.

FIG. 2 is a timing chart of an AC power supply voltage waveform and a rectified output current waveform of a conventional power factor correction circuit.

FIG. 3 is a diagram showing a 1 OOKHz switching waveform in part A of the timing chart shown in FIG. 2.

FIG. 4 is a diagram showing a switching waveform of ΙΟΟΚΗζ in the B part of the timing chart shown in FIG. 2.

FIG. 5 is a circuit configuration diagram showing a power factor correction circuit according to the first embodiment.

FIG. 6 is a timing chart of the input current waveform and switching frequency of the power factor correction circuit according to Embodiment 1.

FIG. 7 is a diagram showing a switching waveform of ΙΟΟΚΗζ in part A of the timing chart shown in FIG. 6.

FIG. 8 is a diagram showing a 20 KHz switching waveform in part B of the timing chart shown in FIG. 6.

FIG. 9 is a detailed circuit configuration diagram of the VCO provided in the power factor correction circuit of the first embodiment. [FIG. 10] FIG. 10 is a timing chart of the input current waveform of the power factor correction circuit of Example 1, the voltage input to the hysteresis comparator, and the switching frequency changed by this voltage.

FIG. 11 is a graph showing the VCO characteristics of the power factor correction circuit of Example 1.

[FIG. 12] FIG. 12 is a diagram showing how the pulse frequency of the PWM comparator changes in accordance with the change in the VCO frequency of the power factor correction circuit of the first embodiment.

FIG. 13 is a timing chart of the switching frequency that varies depending on the input current waveform of the power factor correction circuit of Example 2 and the voltage input to the hysteresis comparator.

FIG. 14 is a detailed circuit configuration diagram of the VCO of the power factor correction circuit according to the third embodiment.

FIG. 15 is a timing chart of the input current waveform of the power factor correction circuit of Example 3, the voltage of the capacitor, and the switching frequency that varies depending on this voltage.

FIG. 16 is a diagram showing an inductance characteristic with respect to a current of the boosting reactor.

FIG. 17 is a circuit configuration diagram showing a power factor correction circuit according to Embodiment 4.

FIG. 18 is a diagram showing a state in which the switching frequency is lowered at light load in the power factor correction circuit of Example 4.

FIG. 19 is a circuit configuration diagram showing a power factor correction circuit according to Embodiment 5.

FIG. 20 is a circuit configuration diagram showing a power factor correction circuit according to Embodiment 6.

FIG. 21 is a circuit configuration diagram showing a power factor correction circuit according to Embodiment 7.

FIG. 22 (a) is a configuration diagram illustrating a first example of a pulse width modulator provided in a control circuit in the power factor correction circuit according to the seventh embodiment. FIG. 22B is a configuration diagram illustrating a second example of the pulse width modulator provided in the control circuit in the power factor correction circuit according to the seventh embodiment.

FIG. 23 is a diagram showing input / output waveforms of a pulse width modulator.

FIG. 24 (a) is a diagram showing a first example of input / output characteristics of a pulse width modulator. FIG. 24

(b) is a diagram showing a second example of the input / output characteristics of the pulse width modulator.

FIG. 25 is a diagram showing waveforms at various parts of the power factor correction circuit according to Embodiment 7.

FIG. 26 is a diagram showing input voltage and input current waveforms of the power factor correction circuit according to Example 7.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a power factor correction circuit according to the present invention will be described in detail with reference to the drawings.

[0020] The power factor correction circuit according to the embodiment sets the switching frequency of the main switch according to the value of the current flowing through the AC power supply, the current flowing through the rectifier circuit, or the current flowing through the main switch, that is, the value of the input current. By changing it, the switching frequency is lowered or the switching operation is stopped at the part where the input current is low. As a result, power loss in the low input current portion is reduced, resulting in small size, high efficiency and low noise.

[Example 1]

FIG. 5 is a circuit configuration diagram showing the power factor correction circuit of the first embodiment. FIG. 6 is a timing chart of the input current waveform and switching frequency of the power factor correction circuit of the first embodiment. Fig. 6 shows that when the input current Ii changes from zero to the maximum value, the switching frequency f of the main switch Q1 changes from zero to ΙΟΟΚΗζ, for example.

[0022] In the first embodiment, when the input current is equal to or lower than the lower limit set current, the switching frequency of the main switch is set to the lower limit frequency (for example, 20 KHz), and when the input current is equal to or higher than the upper limit set current. Is set to the upper limit frequency (for example, ΙΟΟΚΗζ). When the input current is within the range up to the lower limit set current force upper limit set current, the switching frequency of the main switch is gradually changed from the lower limit frequency to the upper limit frequency.

In the power factor correction circuit shown in FIG. 5, the input current is controlled in a sine wave shape so as to approximate the input voltage. Therefore, the current is also maximum near the maximum value of the voltage, and the magnitude of the boosting reactor L1 is determined by this current, the voltage, and the switching frequency of the main switch Q1. For this reason, in order to reduce the booster reactor L1, it is necessary to increase the switching frequency near the maximum current value. Further, the magnetic flux of the boosting rear tuttle L1 is proportional to the current. For this reason, the magnetic flux becomes maximum near the maximum value of the current.

[0024] On the other hand, in the case of the conventional power factor correction circuit using a constant switching frequency, in the portion with the low input voltage shown in FIG. 2 (B section), as shown in FIG. Due to the internal capacity, the voltage when the main switch Q1 is turned off is sinusoidal because less energy is stored in the boost reactor L1. This increases the voltage to the output voltage. However, the loss increases only by refluxing the inside. Therefore, the power factor correction circuit of the first embodiment reduces the switching frequency of the main switch Q1 in the portion where the input current is low (B portion in FIG. 6).

FIG. 7 shows a 1 OOKHz switching waveform in the A part (the input current Ii is near the maximum value) of the timing chart shown in FIG. The timing chart shown in FIG. 7 is the same as the timing chart shown in FIG. 2 because the switching frequency f is ΙΟΟΚΗζ. FIG. 8 shows a switching waveform of 20 KHz in the B part (the part where the input current Ii is low) of the timing chart shown in FIG.

The power factor correction circuit of the first embodiment shown in FIG. 5 differs from the conventional power factor correction circuit shown in FIG. 1 only in the configuration of the control circuit 10. The other configuration shown in FIG. 5 is the same as the configuration shown in FIG. 1, and therefore, the same parts are denoted by the same reference numerals and detailed description thereof is omitted.

The control circuit 10 includes an error amplifier 111, a voltage controlled oscillator (VCO) 115, and a PWM comparator 116. The error amplifier 111 and the PWM comparator 116 are the same as those shown in FIG.

[0028] VC0115 (corresponding to the frequency control unit of the present invention) is connected to the connection point between the negative output terminal P2 of the full-wave rectifier circuit B1 and the current detection resistor R, and is proportional to the current flowing through the current detection resistor R. A triangular wave signal (corresponding to the frequency control signal of the present invention) is generated by changing the switching frequency f of the main switch Q1 according to the voltage value. VC0115 has a voltage frequency conversion characteristic in which the switching frequency f of the main switch Q1 increases as the voltage detected by the current detection resistor R increases!

FIG. 9 is a detailed circuit configuration diagram of the VCO provided in the power factor correction circuit according to the first embodiment. In V C0115, a resistor R1 is connected to the current detection resistor R, and a resistor R2 is connected in series to the resistor R1. The cathode of Zener diode ZD is connected to the connection point between resistors R1 and R2. The anode of the Zener diode ZD

B

It is connected to the power supply terminal b of the hysteresis comparator 115a. The connection point between the resistor R1 and the resistor R2 is connected to the input terminal a of the hysteresis comparator 115a, and the ground terminal c of the hysteresis comparator 115a is connected to the negative electrode of the control power source E and the other end of the resistor R2. The output terminal d of the hysteresis comparator 115a is connected to one terminal of the PWM comparator 116. As shown in FIG. 11, the hysteresis comparator 115a generates a triangular wave signal having a voltage frequency conversion characteristic CV in which the switching frequency f of the main switch Q1 increases as the voltage Ea applied to the input terminal a increases. .

In VC0115 shown in FIG. 9, when the input current Ii shown in FIG. 6 reaches near the maximum value (A part), the voltage of the current detection resistor R increases and the tuner diode ZD breaks down. Therefore, the voltage Ea applied to the input terminal a is equal to the breakdown voltage V of the Zener diode ZD and the control voltage.

Z

The total voltage (V + E) with the source voltage E, that is, the upper limit set voltage is set. Also, input power

B Z B

When the current Ii reaches a low part (B part), the voltage of the current detection resistor R decreases, and the control power E force also flows through the resistor R2 via the Zener diode ZD. For this reason, the input terminal

B

The voltage Ea applied to a is set to the control power supply voltage E, that is, the lower limit set voltage. More

B

When the input current Ii is in the range from the vicinity of the maximum value to the low part, the voltage Ea applied to the input terminal a is within the range of the total voltage (V + E) and the control power supply voltage E.

Z B B

Change gradually.

For this reason, as shown in FIG. 11, the voltage proportional to the input current Ii is equal to or lower than the lower limit set voltage E.

B

If the switching frequency f of the main switch Q1 is the lower limit frequency f

12 (e.g. 20KHz

). When the voltage proportional to the input current Ii is equal to or higher than the upper limit setting voltage (V + E)

Z B

In this case, the switching frequency f of the main switch Q1 is set to the upper limit frequency f (for example, ΙΟΟΚΗζ).

11

Determined. The voltage proportional to the input current is changed from the lower limit set voltage E to the upper limit set voltage (V + E)

B Z B

The switching frequency f of the main switch Q1 is the lower limit frequency f force

It is gradually changed from 12 to the upper limit frequency f.

11

In PWM comparator 116 (corresponding to the pulse width control unit of the present invention), the triangular wave signal from VC0115 is input to the − terminal, and the feedback signal FB from error amplifier 111 is input to the + terminal. As shown in FIG. 12, the PWM comparator 116 is turned on when the feedback signal FB value is equal to or greater than the triangular wave signal value, and is turned off when the feedback signal FB value is less than the triangular wave signal value. Generate a Norse signal. The PWM comparator 116 applies a pulse signal to the main switch Q1, and controls the output voltage of the smoothing capacitor C1 to a predetermined voltage. [0033] In addition, when the feedback signal FB decreases due to the output voltage of the smoothing capacitor CI reaching the reference voltage El, the PWM comparator 116 shortens the pulse-on width at which the value of the feedback signal FB becomes equal to or greater than the value of the triangular wave signal. As a result, the output voltage is controlled to a predetermined voltage. That is, the pulse width is controlled.

[0034] Note that the maximum value and the minimum value of the voltage of the triangular wave signal from VCOl 15 do not change with frequency. For this reason, the ON / OFF duty ratio of the nors signal is determined by the feedback signal FB of the error amplifier 111 regardless of the frequency. Moreover, even if the ON width of the pulse signal changes due to the change of the switching frequency f, the duty ratio of ON / OFF of the pulse signal does not change.

Next, the operation of the power factor correction circuit according to the first embodiment configured as described above will be described with reference to FIGS. Here, only the operation of the control circuit 10 will be described.

[0036] First, the error amplifier 111 generates an error voltage signal by amplifying the error between the voltage of the smoothing capacitor C1 and the reference voltage E1, and outputs the error voltage signal to the feedback signal F.

Output to PWM comparator 116 as B.

On the other hand, VC0115 generates a triangular wave signal in which the switching frequency f of the main switch Q 1 is changed according to the voltage value proportional to the current value flowing through the current detection resistor R.

Here, the operation will be described using the timing chart of FIG. When the input current Ii reaches around the maximum value (for example, time t to t, time t to t), the Zener diode shown in Fig. 9

2 3 6 7

ZD surrenders. For this reason, the voltage Ea applied to the input terminal a is the sum of the breakdown voltage V of the Zener diode ZD and the control power supply voltage E (V + E), that is, the upper limit setting voltage.

Z B Z B

Set to Therefore, the voltage proportional to the input current Ii is higher than the upper limit setting voltage (V + E)

Z B

In this case, VC0115 sets the switching frequency f of the main switch Q1 to the upper limit frequency f (for example,) ζ).

11

[0039] Next, when the input current Ii reaches a low part (for example, time t to t, time t to t),

0 1 4 5

Control power supply shown in Fig. 9 Current flows through resistor R2 via Zener diode ZD

B

. Therefore, the voltage Ea applied to the input terminal a is the control power supply voltage E, that is, the lower limit setting voltage.

B

Set to pressure. For this reason, the voltage proportional to the input current Ii is less than the lower limit setting voltage E.

B

When the switching frequency of the main switch Q1 is The number f is set to the lower limit frequency f (e.g. 20KHz) _c

12

[0040] Furthermore, the input current Ii is near the maximum value and low !, within the range up to the part (eg, time t to t, hour

1 t 2 to t, time t to t), the voltage Ea applied to the input terminal a

3 4 5 6

It gradually changes within the range of the pressure (V + E) and the control power supply voltage E. Therefore, the input current I

Z B B

The voltage proportional to i is within the range from the lower limit set voltage E to the upper limit set voltage (V + E).

B Z B

The switching frequency f of the main switch Q1 is the lower limit frequency f and the upper limit frequency f.

12

It gradually changes until.

11

[0041] Next, when the input current Ii is near the maximum value (for example, time t to t, time t to t),

2 3 6 7

As shown in FIG. 12, the PWM comparator 116 is turned on when the value of the feedback signal FB is equal to or larger than the value of the triangular wave signal having the upper limit frequency f, and the value of the feedback signal FB

11

Upper limit frequency f that turns off when is less than the value of the triangular wave signal with upper limit frequency f

11 11 is generated, and the pulse signal is applied to the main switch Q1.

[0042] On the other hand, when the input current Ii is low and part (eg, time t to t, time t to t), the PWM

0 1 4 5

As shown in FIG. 12, the comparator 116 is turned on when the value of the feedback signal FB is equal to or greater than the value of the triangular wave signal having the lower limit frequency f, and the value of the feedback signal FB is lower than the lower limit.

2

Frequency f

Lower frequency f that is off when less than the value of a triangular wave signal with 12

A pulse signal having 12 is generated, and the pulse signal is applied to the main switch Q1.

[0043] Further, the input current Ii is in the vicinity of the maximum value and low !, the range to the part (for example, time t to t, time t

one two Three

~ T, time t ~ t), the PWM comparator 116

4 5 6 12 Generates a pulse signal with a frequency that gradually changes within the range up to the upper limit frequency f.

11

The pulse signal is applied to the main switch Q1.

[0044] Thus, the power factor correction circuit of Example 1 changes the switching frequency f of the main switch Q1 in accordance with the input current Ii, and decreases the switching frequency f at a portion where the input current Ii is low. Make it. As a result, as shown in FIG. 8, the on-time of the main switch Q1 becomes longer, the current increases, and power can be supplied to the load RL. In addition, switching loss can be reduced because the number of switching operations is reduced.

[0045] In particular, the upper limit frequency is set to 100 kHz, for example, as the switching frequency f of the main switch Q1, and the lower limit frequency is set to 20 kHz, for example, as a frequency that cannot be heard by humans. The other part makes the switching frequency f proportional to the input current Ii. For this reason, switching loss can be reduced, and the frequency becomes lower than the audible frequency, and no unpleasant noise is generated.

[0046] Further, since the magnetic flux of boost booster reactor L1 is proportional to the current, the switching frequency is set to the maximum frequency at the maximum value of the input current. In other parts, even if the frequency is changed in proportion to the input AC power supply voltage Vi, the magnetic flux of the boosting rear tuttle L1 does not exceed the maximum value. For this reason, the boosting reactor L1 is not increased in size, and switching loss can be reduced.

[0047] Further, with respect to the inductance characteristic with respect to the current of the boost reactor L1, as shown in FIG. 16, the inductance value may be increased when the current is small, and the inductance value may be decreased when the current is large. . The energy stored in the boost reactor L1 is represented by (LI ² ) Z2, and is proportional to the inductance value L and the current I. For this reason, even when the current is small, the energy stored in the boost reactor L1 is relatively large. For this reason, the current continuous period of the boost reactor L1 can be increased, and the effective value of the current can be reduced, so that the loss can be further reduced. For example, the characteristics shown in FIG. 16 can be obtained by mixing ferrite powder and amorphous powder and appropriately selecting the mixing ratio thereof.

[0048] Further, since the switching frequency f of the main switch Q1 falls within the range from the lower limit frequency to the upper limit frequency, the generated noise is also dispersed with respect to the frequency, so that the noise can be reduced. Therefore, it is possible to provide a power factor correction circuit that is small, highly efficient, and capable of low noise.

[0049] Thereby, the switching power supply device can be made small and highly efficient. Also, when the power consumption during standby is low, the input current is reduced. When the main switch Q1 is switched at a high frequency, the ratio of switching loss increases and the efficiency decreases. Therefore, if the switching frequency is changed in proportion to the input current, the switching frequency is lowered and switching loss can be reduced at low output power. That is, it is possible to improve the efficiency at the time of low output power (such as standby) and reduce the power consumption of a device such as a television (TV). For example, it is possible to reduce the power consumption at the time of low output power such as a function waiting time of a digitalized television or the like (a state in which a tuner and a control circuit are operated and a program table can be received).

[0050] In addition, in the conventional power factor correction circuit shown in FIG. 1, since the voltage at the positive output terminal P1 of the full-wave rectifier circuit B1 is also taken out, it is necessary to use the control circuit 100 for high withstand voltage. Only In the power factor correction circuit of the first embodiment, since the voltage is extracted from the negative output terminal P2 of the full-wave rectifier circuit B1, the control circuit 10 can be used for a low breakdown voltage.

[0051] (Example 2)

FIG. 13 is a timing chart of the switching frequency that varies depending on the input current waveform of the power factor correction circuit of Example 2 and the voltage input to the VCO.

In Example 1 shown in FIG. 10, when the input current Ii reaches a low portion, VC0115 sets the switching frequency f of the main switch Q1 to the lower limit frequency f (for example, 20 KHz).

12

It was. In Example 2 shown in FIG. 13, when the input current Ii is low, the lower limit frequency f

If it is less than 12, VC0115 stops the operation of main switch Q1. Since the AC power supply current is small at this stop, distortion of the input current waveform is minimized.

[0053] (Example 3)

In Example 3, when the voltage proportional to the input current is below the set voltage, the switching frequency of the main switch is set to the lower limit frequency (for example, 20 KHz), and when the voltage proportional to the input current exceeds the set voltage, The switching frequency of the switch is set to the upper limit frequency (for example, ΙΟΟΚΗζ).

FIG. 14 is a detailed circuit configuration diagram of the VCO of the power factor correction circuit according to the third embodiment. In the VCO 115A shown in FIG. 14, a resistor R1 is connected to the negative output terminal P2 of the full-wave rectifier circuit B1, and a resistor R2 is connected in series to the resistor R1. The comparator 115b inputs the voltage at the connection point between the resistor R1 and the resistor R2 to the + terminal, and inputs the reference voltage Erl to one terminal. The comparator 115b outputs an H level to the base of the transistor TR1 when the voltage at the connection point between the resistor R1 and the resistor R2 is higher than the reference voltage Erl. In this case, the reference voltage Erl is set to the set voltage.

[0055] The emitter of the transistor TR1 is grounded, and the collector of the transistor TR1 is connected to the base of the transistor TR2, one end of the resistor R4, and one end of the resistor R5 via the resistor R3. The other end of the resistor R4 is connected to the power supply V, and the other end of the resistor R5 is grounded. Transistor

B

The emitter of TR2 is connected to power supply V through resistor R6, and the collector of transistor TR2

B

Grounded via capacitor C!

[0056] In order to give hysteresis to the comparator 115c, between the + terminal and the output terminal, Resistor R9 is connected, and the + terminal is grounded through resistor R8.

The comparator 115c inputs the voltage of the capacitor C to the negative terminal. In addition, a series circuit of output terminal force diode D and resistor R7 is connected to one terminal for discharging capacitor C. As shown in Fig. 15, VC0115A sets the switching frequency f of the main switch Q1 to the lower limit frequency f when the voltage proportional to the input current Ii is below the set voltage.

A triangular wave signal set to 12 is generated, and when the voltage proportional to the input current ii exceeds the set voltage, a triangular wave signal with the switching frequency f of the main switch Q1 set to the upper limit frequency f is generated.

11

Generate.

Next, the operation of the power factor correction circuit according to Embodiment 3 configured as described above will be described with reference to FIGS. 14 and 15. Here, only the operation of VC0115A will be described.

First, VC0115A generates a triangular wave signal in which the switching frequency f of the main switch Q 1 is changed according to the voltage value proportional to the current flowing through the current detection resistor R.

Here, the operation will be described with reference to the timing chart of FIG. When the voltage proportional to the input current Ii exceeds the set voltage (e.g., time t to t, time t to t), the comparator 11

2 3 5 6

Transistor TR1 is turned on by H level from 5b. Therefore, from the power supply V to the resistor R4

B

Since the current flows through the resistor R3 via the base of the transistor TR2, the collector current of the transistor TR2 increases. Then, the capacitor C is charged in a short time by the current flowing through the collector of the transistor TR2. That is, since the voltage Ec of the capacitor C rises and this voltage Ec is input to the comparator 115c, the comparator 115c outputs a triangular wave signal in which the switching frequency f of the main switch Q1 is set to the upper limit frequency f (for example, ΙΟΟΚΗζ).

11

Generate.

[0061] On the other hand, when the voltage proportional to the input current Π is equal to or lower than the set voltage (for example, from time t to t

0 to 2 t), H level is not output from comparator 115b, so transistor TR1

3 5

Turn off. For this reason, the collector current of the transistor TR2 decreases, and the charging time of the capacitor C becomes longer. That is, the voltage Ec of the capacitor C rises slowly, and this voltage Ec is input to the comparator 115c, so that the comparator 115c is a triangular wave in which the switching frequency f of the main switch Q1 is set to the lower limit frequency f (for example, 20 KHz). Live signal

12

To do. [0062] Next, when the voltage proportional to the input current Ii exceeds the set voltage (for example, from time t to t

2 to 3), the PWM comparator 116 indicates that the feedback signal FB value is the upper limit frequency f

Turns on when the value is equal to or greater than the value of the triangular wave signal with 5 6 11 and the value of the feedback signal FB is the upper limit frequency f

Upper frequency f that is off when the value is less than the value of the triangular wave signal with 11.

A pulse signal having 11 is generated and the pulse signal is applied to the main switch Q1.

[0063] On the other hand, when the voltage proportional to the input current Ii is equal to or lower than the set voltage (for example, time t to t,

0 2 Time t to t), PWM comparator 116 indicates that the value of feedback signal FB is lower limit frequency f

On when the value of the triangular wave signal with 3 5 1 is greater than or equal to the value of the feedback signal FB

2

Frequency f

A pulse signal having 12 is generated and the pulse signal is applied to the main switch Q1.

[0064] As described above, the power factor correction circuit of Example 3 sets the switching frequency of the main switch Q1 to the lower limit frequency when the voltage proportional to the input current Ii is lower than the set voltage, and sets the input current Ii to the input current Ii. When the proportional voltage exceeds the set voltage, set the switching frequency of the main switch Q1 to the upper limit frequency. For this reason, also in Example 3, the effect almost the same as the effect of Example 1 is acquired.

[0065] Since the input current becomes small at light load, it is only when the voltage proportional to the input current Ii is equal to or lower than the set voltage, and the switching frequency f is the lower limit frequency f (for example, 20

12

KHz) only.

[0066] (Example 4)

FIG. 17 is a circuit configuration diagram showing a power factor correction circuit according to the fourth embodiment. The power factor correction circuit of Example 4 shown in FIG. 17 operates the main switch Q1 at a low frequency (for example, 20 kHz) at a light load such as standby, and operates the main switch Q1 at a high frequency at a normal time (heavy load). Operate at (eg 100kHz). In the fourth embodiment, since only the configuration of the control circuit 10a is different from the control circuit 10 of the first embodiment, only the control circuit 10a will be described.

The control circuit 10a includes an error amplifier 111, an average current detection unit 117, a comparator 118, a VC 0115e, and a PWM comparator 116.

The average current detection unit 117 detects the average value of the current flowing through the current detection resistor R. In comparator 118, the reference voltage VI is input to one terminal, and the average current is detected to the + terminal. The average value of the current is input from the unit 117. The comparator 118 outputs an H level to the VC0115e when the average current value exceeds the reference voltage VI, and outputs an L level to the VC0115e when the average current value is less than or equal to the reference voltage VI.

[0069] VC0115e generates a triangular wave signal with the switching frequency of main switch Q1 set to ΙΟΟΚΗζ when H level is input from comparator 118, and main switch Q 1 when L level is input from comparator 118 A triangular wave signal with a switching frequency set to 20KHz is generated.

[0070] In PWM comparator 116, the triangular wave signal from VC0115e is input to one terminal, and feedback signal FB from error amplifier 111 is input to the + terminal. The PWM comparator 116 generates a pulse signal that is turned on when the value of the feedback signal FB is greater than or equal to the value of the triangular wave signal and turned off when the value of the feedback signal FB is less than the value of the triangular wave signal. The PWM comparator 116 applies the pulse signal to the main switch Q1, and controls the output voltage of the smoothing capacitor C1 to a predetermined voltage.

[0071] According to the above configuration, VC0115e generates a triangular wave signal in which the switching frequency of main switch Q1 is set to ΙΟΟΚΗζ when the average value of the current flowing through current detection resistor R exceeds reference voltage VI. . In this case, as shown in FIG. 18, the switching frequency is set to ΙΟΟΚΗζ at the time of heavy load. VC0115e generates a triangular wave signal with the switching frequency of main switch Q1 set to 20 KHz when the average value of the current falls below the reference voltage VI. In this case, as shown in Fig. 18, the switching frequency is set to 20 KHz at light load. In other words, the main switch Q1 operates at a low frequency (20 kHz) during light loads such as standby, and can operate at a high frequency (100 kHz) during normal (heavy loads).

[0072] Also, in a device such as a television, it is also possible to input a standby signal at the time of standby to the television device side force, and to reduce the switching frequency of the main switch Q1 by this standby signal. In this case, efficiency can be improved only during standby. Furthermore, this standby signal stops the operation of the main switch Q1, and the DCZDC converter connected after the power factor correction circuit supplies power during standby, which can further improve efficiency. In addition, at light loads (such as during standby), the switching frequency is low, so switching loss can be reduced. Efficiency can be improved.

[0073] (Example 5)

FIG. 19 is a circuit configuration diagram showing a power factor correction circuit according to the fifth embodiment. The power factor correction circuit of Example 5 shown in FIG. 19 stops the switching operation of the main switch Q1 when the average value of the current flowing through the current detection resistor R is lower than the set value, and the output voltage of the smoothing capacitor C1 When the voltage falls below the set voltage, the switching operation of the main switch is started. In the fifth embodiment, since the configuration of the control circuit 10b is only different from the control circuit 10 of the first embodiment, only the control circuit 10b will be described.

The control circuit 10b includes an error amplifier 111, an average current detection unit 117, a comparator 119, an OS C114, a comparator 120, and a PWM comparator 116.

The average current detector 117 detects the average value of the current flowing through the current detection resistor R. In the comparator 119, the reference voltage V2 is input to one terminal, and the average value of the current is input from the average current detecting unit 117 to the + terminal. The comparator 119 outputs an H level to the OSC 114 when the average current value exceeds the reference voltage V2, and outputs an L level to the OSC 114 when the average current value becomes the reference voltage V 2 or less.

[0076] When the H level is input from the comparator 119, the OSC 114 generates a triangular wave signal in which the switching frequency of the main switch Q1 is set to 119ζ, and when the L level is input from the comparator 118, the OSC 114 To stop the switching operation, stop the triangular wave signal oscillation operation.

In PWM comparator 116, the triangular wave signal from OSC 114 is input to one terminal, and feedback signal FB from error amplifier 111 is input to the + terminal. The PWM comparator 116 generates a pulse signal that turns on when the value of the feedback signal FB is greater than or equal to the value of the triangular wave signal, and turns off when the value of the feedback signal FB is less than the value of the triangular wave signal. A signal is applied to the main switch Q 1 to control the output voltage of the smoothing capacitor C 1 to a predetermined voltage.

In comparator 120, reference voltage E2 is input to the − terminal, and feedback signal FB from error amplifier 111 is input to the + terminal. The comparator 120 outputs an H level to the OSC 114 when the value of the feedback signal FB is equal to or greater than the value of the reference voltage E2, and When the value of feedback signal FB is less than the value of reference voltage E2, L level is output to OSC 114. Only when the H level is input from the comparator 120, the OSC 114 restarts the oscillation operation of the stopped triangular wave signal and generates a triangular wave signal in which the switching frequency of the main switch Q1 is set to 10 OKHz.

[0079] According to the above configuration, when the average value of the current flowing through the current detection resistor R exceeds the reference voltage V2, the OSC 114 generates a triangular wave signal in which the switching frequency of the main switch Q1 is set to ΙΟΟΚΗζ. When the average value of the current falls below the reference voltage V2, the triangular wave signal oscillation operation is stopped to stop the switching operation of the main switch Q1. OSC114 resumes the oscillation operation of the stopped triangular wave signal only when the value of the feedback signal FB is equal to or higher than the value of the reference voltage E2 (that is, when the output voltage of the smoothing capacitor C1 is lower than the set voltage). To generate a triangular wave signal with the switching frequency of the main switch Q1 set to 100 KHz.

That is, when the average value of the current flowing through the current detection resistor R becomes less than the set value, the switching operation of the main switch Q 1 is stopped, and the output voltage of the smoothing capacitor C 1 becomes less than the set voltage. In this case, since the switching operation of the main switch Q1 is started, the switching loss of the main switch Q1 can be further reduced.

[0081] (Example 6)

FIG. 20 is a circuit configuration diagram showing a power factor correction circuit according to the sixth embodiment. The power factor improvement circuit of Example 6 is a zero current switch when the main switch is turned on by the leakage inductance between the main winding and the return winding wound around the core having the center leg and the side leg ( The loss is reduced by performing ZCS). In addition, this power factor correction circuit achieves high efficiency by returning the energy stored in the leakage inductance to the load via the diode via the magnetic path of the core.

[0082] Further, this power factor correction circuit is a continuous mode boost type power factor correction circuit that converts the input current into a sine wave, controls the voltage of the smoothing capacitor, and supplies power from the smoothing capacitor to the load. Clamp main switch voltage to smoothing capacitor voltage. The continuous mode is an operation mode in which the main switch Q1 is turned on again when the current Dli flows through the diode D1, that is, when the current flows through the main winding 5a. In FIG. 20, a full-wave rectifier circuit B1 is connected to an AC power supply Vac 1 and rectifies an AC power supply voltage of AC power Vacl and outputs it to the positive output terminal P 1 and the negative output terminal P2.

[0084] The boosting reactor tutor L2 has a main power line 5a (number nl) and a feedback power line 5b (number n2) connected in series to the main power line 5a. Wire 5b is electromagnetically coupled. The feedback cable 5b is loosely coupled to the main cable 5a, and the leakage inductance between the main cable 5a and the feedback cable 5b is increased.

[0085] Between the positive-side output terminal P1 and the negative-side output terminal P2 of the full-wave rectifier circuit B1, the main winding 5a of the boosting rear reactor L2, the diode D1, the smoothing capacitor C1, and the current detection resistor R are formed. The first series circuit is connected.

[0086] In addition, a second series circuit including a boosting reactor L2, a main switch Q1, and a current detection resistor R is connected between the positive output terminal P1 and the negative output terminal P2 of the full-wave rectifier circuit B1. It has been done. A diode D2 is connected between the connection point between the main switch Q1 and the feedback feeder 5b and the smoothing capacitor C1.

The configuration of the control circuit 10 is the same as the configuration of the control circuit 10 shown in FIG. 5, and therefore detailed description thereof is omitted here.

Next, the operation of the power factor correction circuit according to Embodiment 6 configured as described above will be described. First, since current flows through main wire 5a, diode D1 is conductive. When the main switch Q1 is turned on, current flows through the path of Vacl → Bl → 5a → 5b → Ql → R → Bl → Vacl due to the voltage obtained by rectifying the AC power supply voltage Vi. For this reason, a voltage is applied to the leakage inductance Le (not shown) of the feedback winding 5b, and the current flowing through the main switch Q1 increases with the slope of EoZLe. Accordingly, since the current of the main switch Q1 starts from zero, the main switch Q1 is in ZCS operation.

Note that, when the diode D1 is in a conductive state, the same voltage as the output voltage Eo (the voltage across the smoothing capacitor C1) is applied to the leakage inductance Le. After the diode D1 is turned off, the voltage of the AC power supply Vacl is applied to the main wire 5a.

[0090] At the same time as the current of the feedback winding 5b increases, the current flowing through the diode D1 decreases to zero, and the diode D1 is turned off. During the recovery time, the diode A spike current due to the recovery of Dl flows to the main switch Ql. This spike current is limited by the impedance of leakage inductance Le.

[0091] The recovery time ends, the reverse direction of the diode D1 recovers, and the rate of increase in the current of the feedback winding 5b decreases. The voltage of the main feeder 5a of the boost reactor L2 is added to the input voltage.

The current Qli flows through the path Vacl → Bl → 5a → 5b → Ql → R → Bl → Vacl. The current in main switch Q1 rises with a slope of VaclZ5a.

[0092] Next, when the main switch Q1 is turned off, the energy stored in the main feeder line 5a of the boosting rear tuttle L2 causes the diode to pass through the path 5a → Dl → Cl → R → Bl → Vacl → 5a. Current flows through D1. For this reason, the smoothing capacitor C1 is charged and power is supplied to the load RL.

[0093] Similarly, the voltage of the main switch Q1 rises due to the energy stored in the feedback feeder 5b. In addition, due to the energy stored in the feedback feeder 5b, a current flows through the diode D2 through the path 5b → D2 → Cl → R → Bl → Vacl → 5a → 5b. In other words, the energy stored in the feedback feeder 5b is regenerated to the load RL via the diode D2. The amount of energy at this time is determined by the voltage generated in the feedback feeder 5b of the boosting reactor and the current of the leakage inductance Le. The greater the number n2 of feedback wires 5b, the higher the generated voltage, and the discharge will be completed in a short time.

[0094] At the time when this discharge is completed, the current of the diode D2 becomes zero. If the main switch Q1 is turned on again after the reverse characteristics are restored, the ZCS operation can be continued. The control circuit 10 controls the on-duty of the main switch Q1 so that the rectified output current waveform is equal to the waveform obtained by full-wave rectification of the AC power supply voltage Vi. it can.

[0095] As described above, according to the power factor correction circuit of Example 6, the spike current caused by diode recovery when the main switch Q1 is turned on by the leakage inductance Le between the main winding 5a and the feedback winding 5b. No longer flows. For this reason, noise is reduced and the noise filter is also miniaturized, so that the switching power supply can be reduced in size and efficiency.

[0096] Further, since the leakage inductance Le allows ZCS to be performed when the main switch Q1 is turned on, switching loss and switching noise can be reduced, so that high efficiency is achieved. , Low noise can be achieved. In addition, high efficiency can be achieved by returning the energy stored in the leakage inductance Le to the load via the magnetic path of the core.

[0097] Further, as in the first embodiment, the control circuit 10 sets the switching frequency of the main switch Q1 to the lower limit frequency (for example, 20KHz) when the input current is equal to or lower than the lower limit set current, and the input current is set to the upper limit. Set the switching frequency of the main switch Q1 to the upper limit frequency (for example, ΙΟΟΚΗζ) when the current is higher than the set current, and set the lower limit of the switching frequency of the main switch Q1 when the input current is within the range up to the upper limit set current. Gradually change from the frequency to the upper frequency limit. For this reason, the same effects as those of the first embodiment can be obtained. Further, the power factor correction circuit shown in FIG. 20 is replaced with the control circuit of the second embodiment having the characteristics shown in FIG. 13 or the control circuit of the third embodiment having the characteristics shown in FIG. Alternatively, the control circuit 10a of the fourth embodiment shown in FIG. 17 or the control circuit 10b of the fifth embodiment shown in FIG. 19 may be used.

[Example 7]

FIG. 21 is a circuit configuration diagram showing a power factor correction circuit according to the seventh embodiment. In the seventh embodiment, the configuration of the control circuit 10d is different from the configuration of the first embodiment. The control circuit 10d includes an output voltage detection operational amplifier 11, a multiplier 12, a current detection operational amplifier 13, and a pulse width modulator 14. The output voltage detection operational amplifier 11 corresponds to the error amplifier 111 of the first embodiment shown in FIG.

The output voltage detection operational amplifier 11 generates an error voltage by amplifying the error between the voltage of the smoothing capacitor C1 and the reference voltage Vref, and outputs the error voltage to the multiplier 12. The multiplier 12 multiplies the error voltage from the output voltage detection operational amplifier 11 by the output of the current detection operational amplifier 13 (input of the pulse width modulator 14), and outputs the multiplied output voltage to the current detection operational amplifier 13.

[0100] The current detection operational amplifier 13 generates an error voltage by amplifying an error between the voltage proportional to the input current detected by the current detection resistor R and the multiplication output voltage from the multiplier 12, and generates the error voltage. Output to the pulse width modulator 14 as a comparison input signal. Further, the current detection operational amplifier 13 feeds back the generated error voltage to the multiplier 12 as described above. Note that the power factor correction circuit of the seventh embodiment uses the multiplier 12 as a voltage variable unit for varying the output of the current detection operational amplifier 13 according to the error voltage from the output voltage detection operational amplifier 11. Yes. In place of the multiplier 12, a divider or a variable gain amplifier can be used.

[0102] The pulse width modulator 14 includes a VC0141 and a comparator 142, as shown in FIG. VC0141 generates a triangular wave signal in which the switching frequency f of the main switch Q1 is changed according to the voltage value proportional to the current flowing through the current detection resistor R. In the comparator 142, the triangular wave signal from the VC0141 is input to the + terminal, and the comparison input signal from the voltage detection operation 13 is input to the − terminal. The comparator 142 is, for example, on (H level) when the value of the triangular wave signal is greater than or equal to the value of the comparison input signal, and is off (L level, for example, when the value of the triangular wave signal is less than the value of the comparison input signal. Zero) is generated, and the pulse signal is applied to the gate of the main switch Q1 to control the output voltage of the smoothing capacitor C1 to a predetermined voltage. VC0141 corresponds to VC Ol 15 of the first embodiment shown in FIG. The comparator 142 corresponds to the PWM comparator 1 16 of the first embodiment shown in FIG.

FIG. 24 (a) and FIG. 24 (b) are diagrams showing an example of input / output characteristics of the pulse width modulator. Figure 24 (a) shows the input / output characteristics of the pulse width modulator in which the input voltage Es and the duty cycle D are in a proportional relationship, and Es = D. Figure 24 (b) shows the input / output characteristics of a pulse width modulator in which the input voltage Es and the duty cycle D are in the relationship Es = l–D.

[0104] In the pulse width modulator 14 shown in Fig. 22 (a), the input / output waveform is a waveform like "Output 1" in Fig. 23. The input / output characteristics of the pulse width modulator 14 are shown in Fig. 24 (a ).

[0105] Further, the comparator 142 is a pulse signal that is turned on, for example, when the value of the comparison input signal is greater than or equal to the value of the triangular wave signal, and turned off, for example, when the value of the comparison input signal is less than the value of the triangular wave signal. Then, the pulse voltage may be applied to the gate of the switch Q1 to control the output voltage of the smoothing capacitor C1 to a predetermined voltage. That is, when “+” and “one” of the input terminal of the comparator 142 shown in FIG. 22 (a) are connected in reverse, the output voltage is inverted. The input / output waveform is as shown in “Output 2” in Fig. 23, and the input / output characteristics are as shown in Fig. 24 (b). become.

FIG. 22 (b) shows another configuration example of the pulse width modulator 14a! /. The pulse width modulator 14 a inverts the comparison input signal with an inverter 143 that also has an operational amplifier force, and supplies it to the negative terminal of the comparator 144. The inverter 143 has a resistor r2 connected between the output terminal and the-terminal, a comparison input signal is input to the-terminal via the resistor rl, and a voltage divided by the resistors r3 and r4 is applied to the + terminal. Is input and the inverted output is output to one terminal of the comparator 142.

According to such a configuration, when the voltage of the comparison input signal is low, the voltage at the negative terminal of the comparator 142 increases. Therefore, the input / output characteristics of the pulse width modulator 14a are as shown in FIG. 24 (b), and the duty cycle D is reduced. When the “+” and “one” of the input terminal of comparator 14 2 shown in Fig. 22 (b) are connected in reverse, the voltage of the comparison input signal is high! Becomes lower. For this reason, the input / output characteristics of the pulse width modulator 14 are as shown in FIG. 24 (a), and the duty cycle D increases when the comparison input signal is at a low voltage.

Next, the operation principle of the power factor correction circuit according to Embodiment 7 will be described. Here, the operation of the control circuit 10d will be described.

[0109] First, it is assumed that the current of the boosting rear tuttle L1 continuously flows. Full-wave rectification when the duty cycle in which the main switch Q1 is on (corresponding to the on-time ratio T2ZT1 when the switching period of the main switch Q1 is T1 and the on-time of the main switch Q1 is T2) is 0 The relationship between the input voltage Ei that is the voltage across circuit B1 and the output voltage Eo that is the voltage across load RL is Eo / Ei = l / (l -D).

[0110] Further, it is assumed that the characteristics of the pulse width modulator 14 are as shown in FIG. When the input voltage of the pulse width modulator 14 is Es, Es = l—D, and Es = l—D = EiZEo.

[0111] The output voltage Eo is a substantially constant value in direct current, and the input voltage Ei is a half-cycle sine wave. Therefore, the input voltage Es is an amplified output of the current detection operational amplifier 13 and becomes a half cycle sine wave. The multiplier 12 converts the voltage obtained by varying the output of the current detection operational amplifier 13 according to the value of the error voltage (DC voltage) from the output voltage detection operational amplifier 11 to the second reference voltage (half-wave sine wave). Output to the current detection operational amplifier 13 as a reference voltage) The The current detection operational amplifier 13 amplifies an error between the voltage Vrs h proportional to the current detected by the current detection resistor R and the half-wave sine wave reference voltage, and outputs the half-wave sine wave to the pulse width modulator 14. To do. For this reason, the input current detected by the current detection resistor R is a half-wave sine wave. Therefore, the input current flowing in the current detection resistor R becomes a half-wave sine wave in proportion to the input voltage Ei, so that the power factor can be improved.

[0112] Since the output voltage from the output voltage detection operational amplifier 11 is input to the other input terminal of the multiplier 12, the multiplier 12 responds to the value of the output voltage from the output voltage detection operational amplifier 11. To change the gain (output). For this reason, the magnitude of the half-wave sine wave voltage input to the pulse width modulator 14 can be changed.

[0113] If the output voltage Eo decreases for some reason, the output voltage detection operation 11 decreases the output voltage in accordance with the decrease of the output voltage Eo. Since the multiplier 12 decreases the gain (output) due to the decrease in the output voltage of the output voltage detection operational amplifier 11, the comparison input signal output from the current detection operational amplifier 13 also decreases, and the pulse width modulator 14 The average duty cycle D of the pulse signal is increased by reducing the comparison input signal from the detection operational amplifier 13 (in the case of output 1 shown in Fig. 23). For this reason, the proportion of time that the main switch Q1 is on increases and the input current increases. Therefore, the output voltage Eo rises and the output voltage Eo is held constant.

Next, the overall operation of the power factor correction circuit will be described with reference to the waveforms of the respective parts in FIG. First, when the sine wave input voltage Vi of the AC power supply Vacl is input, the sine wave input current Ii flows. Then, the input voltage Vi of the AC power supply Vacl is rectified by the full-wave rectifier circuit B1, and the full-wave rectified voltage Ei is output.

[0115] Next, when the main switch Q1 is turned on, a current flows through a route of B1-> L1-> Q1-> R-> B1. Next, when the on-state force changes to the off-state, the main switch Q1 also increases the voltage of the main switch Q1 due to the voltage induced in the boosting rear tuttle L1. Also, since the main switch Q1 is turned off, the current flowing through the main switch Q1 becomes zero. In addition, current flows along the route L1 → D1 → C1, and power is supplied to the load RL.

[0116] By turning on and off the main switch Q1 at the switching frequency in this way, a half-cycle sine wave current flows through both ends of the current detection resistor R. And at one end of multiplier 12 The voltage from the current detection operational amplifier 13 (negative half-cycle sine wave voltage indicated by “multiplier input 2” in FIG. 25) is input. Further, the voltage from the output voltage detection operational amplifier 11 (positive DC voltage indicated by “multiplier input 1” in FIG. 25) is input to the other end of the multiplier 12. The multiplier 12 varies the output of the current detection operational amplifier 13 according to the value of the error voltage (DC voltage) from the output voltage detection operational amplifier 11. The variable voltage becomes a half-wave sine wave reference voltage.

[0117] The current detection operational amplifier 13 amplifies the error between the voltage Vrsh proportional to the current detected by the current detection resistor R and the reference voltage of the half-wave sine wave, and changes the pulse width of the half-wave sine wave. Output to controller 14. As shown in Figure 25, the “current detection operational amplifier output” is output as a half-cycle sine wave output voltage similar to the input.

Next, the “current detection operational amplifier output” shown in FIG. 25 is input to the pulse width modulator 14 to control the pulse width of the pulse signal. At this time, since the pulse width modulator 14 has the characteristics shown in FIG. 24 (b), the duty cycle of the main switch Q1 is as shown in FIG. Figure 26 shows the actual input voltage Vi and input current Ii of this power factor correction circuit. In the waveform shown in Fig. 26, good results were shown for each of the power factor and distortion rate that are very close to a sine wave, with the current near zero current slightly deviating from the sine wave.

As described above, the power factor correction circuit according to the seventh embodiment can improve the power factor and input the output of the current detection operational amplifier 13 to the multiplier 12. This eliminates the need for a resistor to divide the full-wave rectified voltage output from the positive output terminal P1 of the full-wave rectifier circuit B1, and reduces the number of parts compared to the control circuit 100 shown in FIG. It can be configured and is inexpensive and easy to adjust the circuit.

[0120] In addition, the conventional power factor correction circuit shown in Fig. 1 detects current with a current detection resistor R, passes through a current detection operational amplifier 13 and a pulse width modulator 14, and performs PWM control of the main switch Q1. To have a first negative feedback loop for controlling the current. In addition, the conventional power ratio improvement circuit detects the output voltage of the smoothing capacitor C1 and controls the main switch Q1 through the output voltage detection operational amplifier 11, the multiplier 12, the current detection operational amplifier 13, and the pulse width modulator 14. Thus, a second negative feedback loop for controlling the output voltage is provided. Furthermore, the conventional power factor correction circuit detects the voltage from the full-wave rectifier circuit B1, By controlling the main switch Ql through the width modulator 14, it has a third negative feedback loop that controls the output voltage.

In contrast, the power factor correction circuit according to the seventh embodiment can reduce the voltage detection loop that detects the voltage from the full-wave rectifier circuit B1 and inputs the voltage to the multiplier 12 by one. For this reason, the instability of the control circuit 1 Od due to this loop is eliminated, and the circuit can be stably controlled with two loops.

[0122] Further, the VC0141 in the pulse width modulator 14 included in the control circuit 10d allows the switching frequency of the main switch Q1 to be set to the lower limit frequency (for example, when the input current is equal to or lower than the lower limit set current as in the first embodiment). 20KHz). When the input current is equal to or higher than the upper limit set current, the switching frequency of the main switch Q1 is set to the upper limit frequency (for example, ΙΟΟΚΗζ). When the input current is within the range up to the lower limit set current force upper limit set current, the switching frequency of the main switch Q1 is gradually changed from the lower limit frequency to the upper limit frequency. For this reason, the same effect as the effect of Example 1 is obtained. Further, instead of the control circuit lOd, the control circuit according to any one of the second to fifth embodiments may be used.

[0123] As described above, the power factor correction circuit according to the present invention is capable of switching the main switch according to the value of the current flowing through the AC power supply, the current flowing through the rectifier circuit, or the current flowing through the main switch, that is, the input current. By changing the frequency, the switching frequency is lowered or the switching operation is stopped at the part where the input current is low. Therefore, it is possible to reduce the power loss of the low input current portion, and to achieve small size, high efficiency and low noise. As a result, the switching power supply device can be made smaller and more efficient, and the efficiency at the time of low output power (such as standby) can be improved to reduce the power consumption of a device such as a television.

Note that the power factor correction circuit shown in FIG. 20 may be configured by the control circuit 1 Od of the seventh embodiment shown in FIG. 21 instead of the control circuit 10.

Industrial applicability

The power factor correction circuit of the present invention can be applied to an AC-DC conversion type power supply circuit.

Claims

The scope of the claims

[1] A boosting reactor that inputs a rectified voltage obtained by rectifying the AC power supply voltage of the AC power supply using a rectifier circuit;

A main switch that is turned on and off by inputting the rectified voltage via the boosting reactor, and a converter that converts a voltage obtained by turning on and off the main switch into a DC output voltage;

By turning on and off the main switch, the AC power supply current is made sinusoidal, the output voltage of the converter is controlled to a predetermined voltage, and the switching frequency of the main switch is the current flowing through the AC power supply or the rectification A control unit that controls the current flowing through the circuit or the value of the current flowing through the main switch;

Having power factor correction circuit.

[2] A boosting rear tuttle having a main power line and a feedback power line connected in series to the main power line and loosely coupled to the main power line;

A first series circuit that is connected between one output terminal and the other output terminal of a rectifier circuit that rectifies an AC power supply voltage of an AC power supply, and that includes the main winding of the boosting rear tuttle, a first diode, and a smoothing capacitor. When,

A second series circuit connected between the one output terminal and the other output terminal of the rectifier circuit and comprising the main power line, the feedback power line and the main switch of the boosting rear tuttle; and the main switch And a second diode connected between a connection point between the step-up rear tuttle and the feedback feeder and the smoothing capacitor;

By turning on and off the main switch, the AC power supply current is made sinusoidal, the output voltage of the smoothing capacitor is controlled to a predetermined voltage, and the switching frequency of the main switch is changed to the current flowing through the AC power supply or the rectifier. A controller that controls the current flowing in the circuit or the value of the current flowing in the main switch;

Having power factor correction circuit.

[3] The control unit includes:

An error voltage generation unit that generates an error voltage signal by amplifying an error between the output voltage and a reference voltage; A current detector that detects the current flowing through the AC power supply, the current flowing through the rectifier circuit, or the current flowing through the main switch;

A frequency control unit that generates a frequency control signal in which the switching frequency of the main switch is changed in accordance with the value of the current detected by the current detection unit;

A pulse width is controlled based on the error voltage signal of the error voltage generator, and a pulse signal is generated by changing the switching frequency of the main switch according to the frequency control signal generated by the frequency controller. A pulse width controller that applies the pulse signal to the main switch to control the output voltage to a predetermined voltage;

The power factor correction circuit according to claim 1, comprising:

[4] The control unit sets the switching frequency of the main switch to a lower limit frequency when the current flowing through the AC power source, the current flowing through the rectifier circuit, or the current flowing through the main switch is equal to or lower than a lower limit set current. When the current is equal to or higher than the upper limit set current, the switching frequency is set to the upper limit frequency, and when the current is within the range from the lower limit set current to the upper limit set current, the switching frequency is set. The power factor correction circuit according to claim 1 or 2, wherein the power factor is gradually changed from the lower limit frequency to the upper limit frequency.

[5] The control unit sets the switching frequency of the main switch to an upper limit frequency when the current flowing to the AC power source, the current flowing to the rectifier circuit, or the current flowing to the main switch is equal to or higher than an upper limit set current. When the current is within the range from the lower limit set current force to the upper limit set current, the switching frequency is gradually changed from the lower limit frequency to the upper limit frequency, and the current is less than the lower limit set current. The power factor correction circuit according to claim 1 or 2, wherein the switching operation of the main switch is stopped in a case.

[6] The control unit sets the switching frequency of the main switch to the lowest frequency when the current flowing through the AC power source, the current flowing through the rectifier circuit, or the current flowing through the main switch is equal to or lower than a set current. The power factor correction circuit according to claim 1 or 2, wherein the switching frequency is set to a maximum frequency when the current exceeds the set current.

7. The power factor correction circuit according to claim 1, wherein the boosting rear tuttle has a characteristic that an inductance value decreases when a value of a current flowing through the boosting reactor is increased.

[8] When the average value of the current flowing through the AC power source, the current flowing through the rectifier circuit, or the current flowing through the main switch is equal to or lower than a set value, the control unit may switch the switching frequency of the main switch. The power factor correction circuit according to claim 1 or 2, wherein the power factor is reduced.

[9] The control unit performs the switching operation of the main switch when an average value of the current flowing through the AC power source, the current flowing through the rectifier circuit, or the current flowing through the main switch becomes a set value or less. The power factor correction circuit according to claim 1 or 2, wherein the power switch is stopped and the switching operation of the main switch is started when the output voltage becomes equal to or lower than a set voltage.

[10] The control unit includes:

A current detector that detects the current flowing through the AC power supply, the current flowing through the rectifier circuit, or the current flowing through the main switch;

An error voltage generator that generates an error voltage signal by amplifying an error between the output voltage and the first reference voltage;

A current detection amplification unit that outputs a voltage amplification signal by amplifying an error between a voltage proportional to the current detected by the current detection unit and a second reference voltage;

A voltage signal obtained by varying the voltage amplification signal of the current detection amplification unit according to the value of the error voltage signal from the error voltage generation unit is used as the second reference voltage to the current detection amplification unit. A voltage variable section to output;

A pulse signal that controls a pulse width according to the value of the voltage amplification signal of the current detection amplification unit and changes the switching frequency of the main switch according to the frequency control signal generated by the frequency control unit. The power factor correction circuit according to claim 1, further comprising: a pulse width control unit configured to generate and to apply the pulse signal to the main switch to control the output voltage to a predetermined voltage.